Define the Theory or Principle of Drying?
Drying can be illustrated as the application of heat under controlled conditions to eliminate the majority of the water generally available in a food by evaporation. The major aim of dehydration is to extend the shelf life of foods by a reduction in water activity (aw). This will slow down microbial growth, though the processing temperature will not generally be sufficient to cause inactivation, thus care will required to be taken with the product on consequent rehydration. Drying does cause deterioration in the eating quality and nutritive value of the food. The role of the food engineer is to design a plant that will minimize such detrimental effects while obtaining efficient drying rates. Typical foods that are important commercially include; sugar, coffee, milk, potato, flour, beans, pulses, grains, nuts, breakfast cereals, tea and spices. From our discussion above, it is clear that dehydration deals with reduction in the moisture content of foods. In this context, therefore, understanding where and how the water is present, and assessment of moisture content in foods becomes crucial.